There is much to be said for the model with propellers placed near the centers of gravity and pressure. Many authorities believe that the successful aeroplane of the future will carry propellers somewhere near the center of the motor base. Since the thrust is exerted near the point where the aeroplane balances, it is argued that its stability is greatly increased, while with the propellers far removed, either to the front or rear, the torque gains a leverage from its position which it is difficult to control. The main difficulty with this arrangement all along for rubber-strand motors has been that the length of the motor must be cut down to about half, and their efficiency reduced.
In the Canning model, this difficulty has been overcome, and a motor extending the entire length of the motor base is hitched up to twin propellers placed near the center of gravity. A powerful motor extends along the center of the motor base, attached to a gear wheel at the forward end. This wheel turns two smaller gears at either side. In this way, a motor running the entire length of the frame may be used with an increased number of turns. A third gear wheel should be introduced to make the propellers turn in opposite directions.
THE FLEMMING WILLIAMS MODEL.
An immense amount of curiosity has been aroused regarding the famous Flemming Williams model. This machine has completely outdistanced all rivals, and set a new and amazing distance record. Its builder frequently gets flights of eighteen hundred feet with his model, and has made the astonishing record, under favorable conditions, of one-half a mile. In order to study this model at first hand, the writer has imported one of the machines, built by Ding, Sayles & Company, one of the leading model builders of England.
The distance qualities of this model will be recognized at a glance. It is a single sticker, extremely light in all its members, combining an extraordinarily long motor base with well-adjusted plane surfaces. The arrangement of the wings is original. The main stability plane is set forward in front of the center of pressure. The rear plane is formed by filling in the space between the rear stick and the braces, thus saving the weight of the frame usually carried in this position. The model is driven by two seven and a half inch propellers of very high pitch. The model is without skids and is launched from the hand.
The central member measures four feet two inches in length. The stick is one-half by one-fourth of an inch, with the forward part tapering gradually to one-fourth of an inch square. The base stick is eight inches in length, cut from a strip five-eighths by one-eighth of an inch. The diagonal pieces forming the triangle are cut from the same material, and meet at a point eight inches from the rear, thus affording a surface of twenty-four square inches. The wooden parts are glued and tied together, no nails or brads being used.
The main plane is an exceedingly refined piece of workmanship. A glance shows that it is very speedy. The frame consists of steel wire one thirty-second of an inch in diameter. The plane measures sixteen and one-half inches in width and four and one-half inches in depth at the narrowest point at the center, and five and one-half inches in the widest part at the ends. It has four cross ribs of the same wire. The frame is covered, on the upper side, with oiled silk. The camber is slightly higher at the sides than the middle.
The plan of fixing a rigid shaft for the propeller axle is very simple and effective. A piece of aluminum tubing is forced over the ends of the rear stick and glued firmly in position. A hole for the axle is then drilled through this tube, and the wooden stick which forms its core. The axle thus turns in what is really a metal shaft, and the friction is reduced to a minimum. A piece of tin tubing, a putty blower, for instance, will serve as well. In this particular machine, the propellers are cut from a board one-sixteenth of an inch thick and bent by steaming to the desired curve.
The shafts of the propellers are formed of a very light steel wire, less than one thirty-second of an inch in diameter. This is passed through the hole in the rear stick and bent into a hook in the usual way. The motor anchorage consists of a wire passed through the central stick and bent back, and turned into two hooks. The rubber-strand motor consists of twenty strands of strip rubber one-eighth of an inch broad. A special preparation resembling cosmoline is used to lubricate the rubber, thus increasing the number of turns. The motor will take on one thousand turns without undue strain.